>Why is reaching every corner of the phone such a big deal anyway?
It's a big deal because the upper left corner is where Android places notifications and thus you're likely to perform this operation frequently and in a number of contexts. Whenever you get a notification you're very likely to want to evaluate it (and possibly take action) as quickly and reliably as possible. On my Nexus 5 I can easily unlock, swipe down and swipe left or tap with one hand and very quickly as well. On my OnePlus One unlocking is fine, but getting to the top left corner is tricky, slow and unreliable when I'm using one hand, and two hands is not always desirable or practical depending on the context.
On my Galaxy Nexus you can swipe down on the entire top edge of the phone to bring down notifications. On the home screen you can actually swipe down anywhere to bring it down.
It's a big deal because the upper left corner is where Android places notifications and thus you're likely to perform this operation frequently and in a number of contexts. Whenever you get a notification you're very likely to want to evaluate it (and possibly take action) as quickly and reliably as possible. On my Nexus 5 I can easily unlock, swipe down and swipe left or tap with one hand and very quickly as well. On my OnePlus One unlocking is fine, but getting to the top left corner is tricky, slow and unreliable when I'm using one hand, and two hands is not always desirable or practical depending on the context.